Hydrogenated amorphous silicon (a-Si:H) is recently emerging as a promising material to provide microchips with passive and active photonic functions through a back-end and CMOS-compatible technological process. In this paper, we discuss the performances achieved with different configurations of a-Si:H-based electro-optical amplitude modulators integrated into passive waveguides. All of the analyzed devices are based on the plasma dispersion effect, a phenomenon that allows to reach useful performances at the communication wavelengths of λ~1.55 μm. Mixed electro-optic simulations, in both steady state and transient conditions, for optimized active photonic devices are finally presented.